Yes, the symmetric key (generated on the fly) is in memory while the data is being recorded, this is the case for every encryption technique. In the public/priv

Yes, the symmetric key (generated on the fly) is in memory while the data is being recorded, this is the case for every encryption technique. In the public/private scheme, once the symmetric key is no longer needed, you discard it permanently and files are only accessible using the private key, which you never had. A symmetric key is 256 bits, an HD video is on the order of hundreds of millions to billions of bits, so even if your public key crypto system were 100,000x slower than the symmetric crypto system, it's still going to be negligible compared to the cost of decrypting the remainder of the data. See https://en.wikipedia.org/wiki/Hybrid_cryptosystem https://en.wikipedia.org/wiki/Hybrid_cryptosystem For this reason, public/private key systems for data at rest is probably not particularly ineffcient relative to your suggestion of a symmetric FDE, plus it has the additional benefit that if you want to operate without the ability to decrypt data at rest, you have that option (by leaving the private key at home, since you only need the public key to write new data).